This invention relates to incremental redundancy transmission in a communication system, and more particularly, time slotted communication systems.
Link layer recovery protocols are used for error and loss recovery in data communication systems. Link layer recovery is especially crucial for wireless communications due to the particularly harsh loss and error characteristics of the link.
When a lost data frame is retransmitted, the receiver may combine the multiple received copies of the frame to increase the likelihood of correct decoding. Alternately, the transmitter may transmit additional parity information instead of retransmitting another copy of the lost frame. These methods of incremental redundancy transmission and soft combining are well known in the art.
Despite having performance potential, these methods have not found an application in practical systems. To enable efficient transmission, (that is, high rate coding), it is required that the protocol permits the transmission of proportionally small amounts of incremental parity information.
The problems associated with the efficient transmission were addressed in a paper, xe2x80x9cA Proposal for IS-136+ Data Servicesxe2x80x9d by Robert Van Nobelen and Nambirajan Seshadri of ATandT Laboratories and Krishna Balachandran, Richard Ejzak and Sanjiv Nanda of Bell Labs, Lucent Technologies Inc. attached herewith as Appendix I, the disclosure of which is hereby incorporated by reference. The paper proposed that the problem be handled by breaking up an uncoded data frame into D blocks, and introducing P parity blocks. Initially, all data blocks that constitute a frame are transmitted. If the receiver is unable to reconstruct, the transmitted frame parity blocks are transmitted one at a time until the receiver is able to recover the frame. If all P parity frames are transmitted, the corresponding coding rate is       D          D      +      P        .
Practical implementation of the proposed procedure requires transmission of frame and block sequence numbers for each block. In addition, variable sized blocks are used at different modulation formats (e.g., QPSK, 8 PSK and 16 PSK).
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.
In accordance with the present invention, there is provided a system and method for designing an incremental redundancy, adaptive modulation data communication system using a time slotted communication channel. The method performs the steps of establishing a time slot having at least one sub-slot with a fixed size and establishes a data block sized to fit in the sub-slot. A header is established having a data block sequence number in the header for the time slot. A parity block is also established which is sized smaller than the data block such that the parity block and data block sequence number fit within the sub-slot. The data block and parity block are transmitted in a sub-slot within the time slot. The method further performs the step of identifying, in the header for the time slot, the number of data blocks and parity blocks transmitted.
Stated generally, the present invention encompasses an incremental redundancy transmission communication system. The system comprises a time slot signal generator that creates a time slot signal having at least one sub-slot with a fixed size and a data block signal generator that creates a data block signal sized to fit in the time slot. A header adder that generates a header having a data block signal sequence number in the header for the time slot signal is also provided. A receiver is also provided that identifies in the header for the time slot signal, a number of data block signals consecutively transmitted.
The present invention further encompasses a method for incremental redundancy transmission in a communication system that uses radio (or retransmission) protocol link frames. The method comprises the step of creating a time slot signal having at least one sub-slot with a fixed size, creating a data block signal sized to fit in the sub-slot, establishing a header having a data block signal sequence number in the header for the time slot signal and identifying in the header for the time slot signal, the number of data block signals consecutively transmitted. The steps of providing, in a header of the time slot signal, a data block sequence number for a first data block signal in a sequence of data block signals and creating a parity block signal smaller than the data block signal such that the parity block signal sequence number fits within the sub-slot signal are also provided.
These and other features and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings and the appended claims.